Media gateways and other switching apparatus are employed to switch TDM and other types of data in, for example, a circuit-switched network. They are often designed for specific needs, such as known or projected traffic demands of one or more PSTN networks, as well as various protocols associated with one or more networks.
Class 4 and class 5 switches use multiple signaling schemas to communicate physical line status and route information. Information communicated between two switches may be sent in-band (on the physical line) or out-of-band (using a separate digital channel). In either case, the signaling information contains two separate and unique items: the physical line signaling information (commonly referred to as the line signal information) and the route information (commonly referred to as the register signal information).
For example, channel-associated-signaling (CAS) involves the transmission of signaling information associated with a voice channel. Signaling System R2 (R2) is a CAS system that includes line signaling and register signaling. An originating port sends “forward signals” in a direction towards the called party and receives “backward signals” in a direction towards the calling party. By this convention, a terminating port sends backward signals in a direction towards the calling party, and receives forward signals in a direction towards the called party. An originating port or calling party may also be referred to herein as the originating party, the origin, the source, the outgoing switch, egress, and the like. A terminating port or called party may also be referred to herein as the terminating party, the destination, the incoming switch, ingress, and the like.
In a general sense, CAS line signaling (e.g., in an R2 system) employs a signaling channel to send and receive four bit values (e.g., “ABCD”). For example, an E1 facility transmits the bit values via “timeslot 16,” whereas a T1 facility robs bits from each time slot (e.g., robs 4 bits from each of 24 PCM samples) to accomplish the same objective.
The ITU/CEPT has standardized an inter-nation form of R2. However, there is no multinational standard for R2 signaling regarding calls that originate and terminate within a single nation's borders. Consequently, a large variety of R2 national variants have developed over the past several decades. Thus, the assignment of the ABCD signals to the standard call-progress events are quite different for each R2 variant within a specific country, and even more different from one country to the next. The wide variation of R2 variants also presents complexities during register signaling.
For example, the information contained within the line signal information and the register signal information includes both standard and non-standard information. Thus, for example, a switch is often required to implement the signaling in several fragments: one fragment to handle the standard information, and several fragments to handle the non-standard, different variations of each signaling method.
Consequently, CAS signaling systems (and specifically R2 systems) are generally designed for the individual variants that are specific to the country or region in which the CAS signaling system will operate. However, due to the large number of different variants, designing the system for the particular combination of variants corresponding to the country or region is exceedingly complex, possibly requiring thousands of man-hours. Similar complexities exist with non-CAS systems, such as common channel signaling (CCS) systems like ISDN/PRI and SS7 systems, among others, as well as other signaling systems.